ObservableCollection dependency property does not update when item in collection is deleted

Question

I have a attached property of type ObservableCollection on a control. If I add or remove items from the collection, the ui does not update. However if I replace the collecti

Answer 1

This is just to add to the answer by Thomas. In my code I do interact with the DependencyObject's properties by creating a handler object localy like below:

private static void OnSpecialDaysChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
{
    var action = new NotifyCollectionChangedEventHandler(
            (o, args) =>
                {
                    var calendar = d as RadCalendar;

                    if (calendar!= null)
                    {
                        // play with calendar's properties/methods
                    }
                });

    if (e.OldValue != null)
    {
       var coll = (INotifyCollectionChanged)e.OldValue;
       // Unsubscribe from CollectionChanged on the old collection
       coll.CollectionChanged -= action;
    }

    if (e.NewValue != null)
    {
       var coll = (ObservableCollection)e.NewValue;
       // Subscribe to CollectionChanged on the new collection
       coll.CollectionChanged += action;
    }
}

Hope this is helpful to someone.